1. Field of the Invention
The present invention relates generally to aerodynamic probes, and in particular to a low aspect ratio flow angle probe with no moving parts.
2. Description of Related Art
The flow of air around an aircraft is of the utmost importance in designing an aircraft and predicting its performance characteristics in various flight conditions. For this reason, flow angle probes were developed to measure the direction of an airflow field directly adjacent the aircraft for critical locations on the aircraft, such as the wing, tail, fuselage, and so forth. Conventional flow angle probes use a pivoting weather vane mechanism to determine the direction of the flow regime at the probe. Using many of these flow angle probes, a flow field can be established for a given flight condition (Mach number, dynamic pressure, angle of attack, angle of sideslip, etc.). By performing many tests and accumulating enough data, the aircraft can be characterized and future conditions can be predicted.
However, the conventional flow angle probes can result in unsatisfactory data due to their inherent limitations. First, a weather vane type probe is relatively bulky and limits how small a region can be evaluated. These conventional flow angle probes have a high aspect ratio and can affect the local flow regime, thereby countering the objective of measuring the local flow sans probe. In confined spaces, probes with moving elements may not fit or function properly. Further, the weather vane type of flow angle probe is ill-suited for transonic and supersonic regimes where many military and space aircraft fly. Local shock waves may be introduced prematurely by such probes due to their high aspect ratio. Accordingly, there is a need for a robust and dependable flow angle probe that does not have any moving parts and has a low aspect ratio, with the capability for measuring flow in a very small space.
The present invention is a flow angle probe that is force-based, i.e., it measures a force on a fin and converts the force to a strain at the base of the probe. The magnitude of the strain can be correlated to a flow direction and velocity from static load calibrations. The probe is small and can be used in tight areas to measure local flow regimes. It is comprised of a small, aerodynamically shaped low aspect ratio fin that has a symmetric airfoil section and a wedge shaped leading and trailing edge. Four strain gauges are mounted on the upper and lower surfaces of the neck between the fin and the mounting base, and the four strain gauges are inter-connected to form a full Wheatstone bridge. The strain gauges on the probe measure the strain on the fin. The output strain is correlated to the normal force on the fin, which in turn is converted to a local flow angle.